The present invention relates to a strip stock feed apparatus for use in presses, and in particular to an adjustable double roll lift system for separating the roll pairs independently of each other.
Strip stock material, such as sheet steel and other materials, is generally fed off supply coils into the press through a pair of opposing rolls, which are driven in intermittent fashion by a power take-off from the press crankshaft. The rolls are urged toward each other so that they frictionally grip the stock as they rotate, which causes a length of the stock to be advanced into the press. In order to permit the stock to be properly aligned within the dies, as by pilots engaging pilot holes in a progressive die operation, it is necessary for the feed rolls to separate at a time just before the moving die comes into contact with the stock. A variety of mechanisms have been used in the past to accomplish this, such as cam lift mechanisms and mechanisms operated by hydraulic or pneumatic cylinders. One such lifting mechanism is disclosed in U.S. Pat. No. 3,782,618, which is owned by the assignee of the present application and is incorporated herein by reference. This mechanism incorporates a double acting piston that is rigidly connected to one of the feed rolls and urges the feed roll against the stock by means of hydraulic pressure developed on one side thereof. A cam is rotated in synchronism with the crankshaft of the press and actuates a plunger that displaces hydraulic fluid against the other side of the piston to separate the feed rolls at a particular time in the press cycle. No provisions are provided for adjusting the angular position of the cam on its shaft, however.
In running certain types of stock in the press, a single pair of rolls on the infeed side of the press is often not satisfactory. For example, in the case where very thick stock is being run, the infeed rolls may not be able to develop sufficient force or frictional gripping action to advance the stock quickly and accurately into the press. A more common situation is where very thin stock is being run, and the action of the infeed rolls in pushing the stock into the press causes it to buckle thereby producing a misfeed which can result in damage to the dies. Even in situations where the stock is sufficiently thick that it does not buckle when being pushed into the press by the infeed rolls, so much material may be removed therefrom by the dies that a very poor skeleton results. The skeleton may not have sufficient integrity to retain its shape as it is being pushed through the press so that it may buckle thereby causing a misfeed or interfering with the rewinding or chopping of the skeleton.
To avoid the problems discussed above when running very thick or thin stock or when the skeleton is poor, it is common practice to employ two pairs of rolls, one on the infeed side and the other on the outfeed side so that the stock is both pushed and pulled through the press. Since a certain amount of synchronization of the infeed and outfeed roll pairs is necessary, the roll lifters have typically been mechanically linked by a cross shaft, which is a large rotatable shaft that runs above or alongside the press between the infeed and outfeed units. As can be appreciated, such a mechanical structure is large and unwieldy and difficult to mount.
In some cases, it is desirable to separate the outfeed rolls at a different time than the infeed rolls. For example, in some cases it is desirable to close the infeed rolls slightly in advance of the outfeed rolls to avoid elongation of the stock.